/*
 * This file is part of aion-emu <aion-emu.com>.
 *
 * aion-emu is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * aion-emu is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with aion-emu.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.aionemu.commons.utils;

import java.util.Random;

/**
 * @author David Beaumont, Copyright 2005
 *         <p/>
 *         A Java implementation of the MT19937 (Mersenne Twister) pseudo random number generator algorithm based upon
 *         the original C code by Makoto Matsumoto and Takuji Nishimura (see <a
 *         href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html">
 *         http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html</a> for more information.
 *         <p/>
 *         As a subclass of java.util.Random this class provides a single canonical method next() for generating bits in
 *         the pseudo random number sequence. Anyone using this class should invoke the public inherited methods
 *         (nextInt(), nextFloat etc.) to obtain values as normal. This class should provide a drop-in replacement for
 *         the standard implementation of java.util.Random with the additional advantage of having a far longer period
 *         and the ability to use a far larger seed value.
 *         <p/>
 *         This is <b>not</b> a cryptographically strong source of randomness and should <b>not</b> be used for
 *         cryptographic systems or in any other situation where true random numbers are required.
 *         <p/>
 *         <!-- Creative Commons License --> <a href="http://creativecommons.org/licenses/LGPL/2.1/"><img
 *         alt="CC-GNU LGPL" border="0" src="http://creativecommons.org/images/public/cc-LGPL-a.png" /></a><br />
 *         This software is licensed under the <a href="http://creativecommons.org/licenses/LGPL/2.1/">CC-GNU LGPL</a>.
 *         <!-- /Creative Commons License --> <!-- <rdf:RDF xmlns="http://web.resource.org/cc/"
 *         xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <Work
 *         rdf:about=""> <license rdf:resource="http://creativecommons.org/licenses/LGPL/2.1/" /> <dc:type
 *         rdf:resource="http://purl.org/dc/dcmitype/Software" /> </Work> <License
 *         rdf:about="http://creativecommons.org/licenses/LGPL/2.1/"> <permits
 *         rdf:resource="http://web.resource.org/cc/Reproduction" /> <permits
 *         rdf:resource="http://web.resource.org/cc/Distribution" /> <requires
 *         rdf:resource="http://web.resource.org/cc/Notice" /> <permits
 *         rdf:resource="http://web.resource.org/cc/DerivativeWorks" /> <requires
 *         rdf:resource="http://web.resource.org/cc/ShareAlike" /> <requires
 *         rdf:resource="http://web.resource.org/cc/SourceCode" /> </License> </rdf:RDF> -->
 * @version 1.0
 */
public class MTRandom extends Random
{
	/**
	 * Auto-generated serial version UID. Note that MTRandom does NOT support serialisation of its internal state and it
	 * may even be necessary to implement read/write methods to re-seed it properly. This is only here to make Eclipse
	 * shut up about it being missing.
	 */
	private static final long	serialVersionUID	= -515082678588212038L;

	// Constants used in the original C implementation
	private final static int	UPPER_MASK			= 0x80000000;
	private final static int	LOWER_MASK			= 0x7fffffff;
	private final static int	N					= 624;
	private final static int	M					= 397;
	private final static int[]	MAGIC				= { 0x0, 0x9908b0df };
	private final static int	MAGIC_FACTOR1		= 1812433253;
	private final static int	MAGIC_FACTOR2		= 1664525;
	private final static int	MAGIC_FACTOR3		= 1566083941;
	private final static int	MAGIC_MASK1			= 0x9d2c5680;
	private final static int	MAGIC_MASK2			= 0xefc60000;
	private final static int	MAGIC_SEED			= 19650218;
	private final static long	DEFAULT_SEED		= 5489L;

	// Internal state
	private transient int[]		mt;
	private transient int		mti;
	private transient boolean	compat				= false;

	// Temporary buffer used during setSeed(long)
	private transient int[]		ibuf;

	/**
	 * The default constructor for an instance of MTRandom. This invokes the no-argument constructor for
	 * java.util.Random which will result in the class being initialised with a seed value obtained by calling
	 * System.currentTimeMillis().
	 */
	public MTRandom()
	{
	}

	/**
	 * This version of the constructor can be used to implement identical behaviour to the original C code version of
	 * this algorithm including exactly replicating the case where the seed value had not been set prior to calling
	 * genrand_int32.
	 * <p/>
	 * If the compatibility flag is set to true, then the algorithm will be seeded with the same default value as was
	 * used in the original C code. Furthermore the setSeed() method, which must take a 64 bit long value, will be
	 * limited to using only the lower 32 bits of the seed to facilitate seamless migration of existing C code into Java
	 * where identical behaviour is required.
	 * <p/>
	 * Whilst useful for ensuring backwards compatibility, it is advised that this feature not be used unless
	 * specifically required, due to the reduction in strength of the seed value.
	 * 
	 * @param compatible
	 *            Compatibility flag for replicating original behaviour.
	 */
	public MTRandom(boolean compatible)
	{
		super(0L);
		compat = compatible;
		setSeed(compat ? DEFAULT_SEED : System.currentTimeMillis());
	}

	/**
	 * This version of the constructor simply initialises the class with the given 64 bit seed value. For a better
	 * random number sequence this seed value should contain as much entropy as possible.
	 * 
	 * @param seed
	 *            The seed value with which to initialise this class.
	 */
	public MTRandom(long seed)
	{
		super(seed);
	}

	/**
	 * This version of the constructor initialises the class with the given byte array. All the data will be used to
	 * initialise this instance.
	 * 
	 * @param buf
	 *            The non-empty byte array of seed information.
	 * @throws NullPointerException
	 *             if the buffer is null.
	 * @throws IllegalArgumentException
	 *             if the buffer has zero length.
	 */
	public MTRandom(byte[] buf)
	{
		super(0L);
		setSeed(buf);
	}

	/**
	 * This version of the constructor initialises the class with the given integer array. All the data will be used to
	 * initialise this instance.
	 * 
	 * @param buf
	 *            The non-empty integer array of seed information.
	 * @throws NullPointerException
	 *             if the buffer is null.
	 * @throws IllegalArgumentException
	 *             if the buffer has zero length.
	 */
	public MTRandom(int[] buf)
	{
		super(0L);
		setSeed(buf);
	}

	// Initializes mt[N] with a simple integer seed. This method is
	// required as part of the Mersenne Twister algorithm but need
	// not be made public.
	/**
	 * @param seed
	 * 
	 */
	private void setSeed(int seed)
	{

		// Annoying runtime check for initialisation of internal data
		// caused by java.util.Random invoking setSeed() during init.
		// This is unavoidable because no fields in our instance will
		// have been initialised at this point, not even if the code
		// were placed at the declaration of the member variable.
		if(mt == null)
			mt = new int[N];

		// ---- Begin Mersenne Twister Algorithm ----
		mt[0] = seed;
		for(mti = 1; mti < N; mti++)
		{
			mt[mti] = (MAGIC_FACTOR1 * (mt[mti - 1] ^ (mt[mti - 1] >>> 30)) + mti);
		}
		// ---- End Mersenne Twister Algorithm ----
	}

	/**
	 * This method resets the state of this instance using the 64 bits of seed data provided. Note that if the same seed
	 * data is passed to two different instances of MTRandom (both of which share the same compatibility state) then the
	 * sequence of numbers generated by both instances will be identical.
	 * <p/>
	 * If this instance was initialised in 'compatibility' mode then this method will only use the lower 32 bits of any
	 * seed value passed in and will match the behaviour of the original C code exactly with respect to state
	 * initialisation.
	 * 
	 * @param seed
	 *            The 64 bit value used to initialise the random number generator state.
	 */
	@Override
	public final synchronized void setSeed(long seed)
	{
		if(compat)
		{
			setSeed((int) seed);
		}
		else
		{

			// Annoying runtime check for initialisation of internal data
			// caused by java.util.Random invoking setSeed() during init.
			// This is unavoidable because no fields in our instance will
			// have been initialised at this point, not even if the code
			// were placed at the declaration of the member variable.
			if(ibuf == null)
				ibuf = new int[2];

			ibuf[0] = (int) seed;
			ibuf[1] = (int) (seed >>> 32);
			setSeed(ibuf);
		}
	}

	/**
	 * This method resets the state of this instance using the byte array of seed data provided. Note that calling this
	 * method is equivalent to calling "setSeed(pack(buf))" and in particular will result in a new integer array being
	 * generated during the call. If you wish to retain this seed data to allow the pseudo random sequence to be
	 * restarted then it would be more efficient to use the "pack()" method to convert it into an integer array first
	 * and then use that to re-seed the instance. The behaviour of the class will be the same in both cases but it will
	 * be more efficient.
	 * 
	 * @param buf
	 *            The non-empty byte array of seed information.
	 * @throws NullPointerException
	 *             if the buffer is null.
	 * @throws IllegalArgumentException
	 *             if the buffer has zero length.
	 */
	public final void setSeed(byte[] buf)
	{
		setSeed(pack(buf));
	}

	/**
	 * This method resets the state of this instance using the integer array of seed data provided. This is the
	 * canonical way of resetting the pseudo random number sequence.
	 * 
	 * @param buf
	 *            The non-empty integer array of seed information.
	 * @throws NullPointerException
	 *             if the buffer is null.
	 * @throws IllegalArgumentException
	 *             if the buffer has zero length.
	 */
	public final synchronized void setSeed(int[] buf)
	{
		int length = buf.length;
		if(length == 0)
			throw new IllegalArgumentException("Seed buffer may not be empty");
		// ---- Begin Mersenne Twister Algorithm ----
		int i = 1, j = 0, k = (N > length ? N : length);
		setSeed(MAGIC_SEED);
		for(; k > 0; k--)
		{
			mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >>> 30)) * MAGIC_FACTOR2)) + buf[j] + j;
			i++;
			j++;
			if(i >= N)
			{
				mt[0] = mt[N - 1];
				i = 1;
			}
			if(j >= length)
				j = 0;
		}
		for(k = N - 1; k > 0; k--)
		{
			mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >>> 30)) * MAGIC_FACTOR3)) - i;
			i++;
			if(i >= N)
			{
				mt[0] = mt[N - 1];
				i = 1;
			}
		}
		mt[0] = UPPER_MASK; // MSB is 1; assuring non-zero initial array
		// ---- End Mersenne Twister Algorithm ----
	}

	/**
	 * This method forms the basis for generating a pseudo random number sequence from this class. If given a value of
	 * 32, this method behaves identically to the genrand_int32 function in the original C code and ensures that using
	 * the standard nextInt() function (inherited from Random) we are able to replicate behaviour exactly.
	 * <p/>
	 * Note that where the number of bits requested is not equal to 32 then bits will simply be masked out from the top
	 * of the returned integer value. That is to say that:
	 * <p/>
	 * 
	 * <pre>
	 * mt.setSeed(12345);
	 * int foo = mt.nextInt(16) + (mt.nextInt(16) &lt;&lt; 16);
	 * </pre>
	 * 
	 * <p/>
	 * will not give the same result as
	 * <p/>
	 * 
	 * <pre>
	 * mt.setSeed(12345);
	 * int foo = mt.nextInt(32);
	 * </pre>
	 * 
	 * @param bits
	 *            The number of significant bits desired in the output.
	 * @return The next value in the pseudo random sequence with the specified number of bits in the lower part of the
	 *         integer.
	 */
	@Override
	protected final synchronized int next(int bits)
	{
		// ---- Begin Mersenne Twister Algorithm ----
		int y, kk;
		if(mti >= N)
		{ // generate N words at one time

			// In the original C implementation, mti is checked here
			// to determine if initialisation has occurred; if not
			// it initialises this instance with DEFAULT_SEED (5489).
			// This is no longer necessary as initialisation of the
			// Java instance must result in initialisation occurring
			// Use the constructor MTRandom(true) to enable backwards
			// compatible behaviour.

			for(kk = 0; kk < N - M; kk++)
			{
				y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
				mt[kk] = mt[kk + M] ^ (y >>> 1) ^ MAGIC[y & 0x1];
			}
			for(; kk < N - 1; kk++)
			{
				y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
				mt[kk] = mt[kk + (M - N)] ^ (y >>> 1) ^ MAGIC[y & 0x1];
			}
			y = (mt[N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK);
			mt[N - 1] = mt[M - 1] ^ (y >>> 1) ^ MAGIC[y & 0x1];

			mti = 0;
		}

		y = mt[mti++];

		// Tempering
		y ^= (y >>> 11);
		y ^= (y << 7) & MAGIC_MASK1;
		y ^= (y << 15) & MAGIC_MASK2;
		y ^= (y >>> 18);
		// ---- End Mersenne Twister Algorithm ----
		return (y >>> (32 - bits));
	}

	// This is a fairly obscure little code section to pack a
	// byte[] into an int[] in little endian ordering.

	/**
	 * This simply utility method can be used in cases where a byte array of seed data is to be used to repeatedly
	 * re-seed the random number sequence. By packing the byte array into an integer array first, using this method, and
	 * then invoking setSeed() with that; it removes the need to re-pack the byte array each time setSeed() is called.
	 * <p/>
	 * If the length of the byte array is not a multiple of 4 then it is implicitly padded with zeros as necessary. For
	 * example:
	 * <p/>
	 * 
	 * <pre>
	 *     byte[] { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06 }
	 * </pre>
	 * 
	 * <p/>
	 * becomes
	 * <p/>
	 * 
	 * <pre>
	 *     int[]  { 0x04030201, 0x00000605 }
	 * </pre>
	 * 
	 * <p/>
	 * <p/>
	 * Note that this method will not complain if the given byte array is empty and will produce an empty integer array,
	 * but the setSeed() method will throw an exception if the empty integer array is passed to it.
	 * 
	 * @param buf
	 *            The non-null byte array to be packed.
	 * @return A non-null integer array of the packed bytes.
	 * @throws NullPointerException
	 *             if the given byte array is null.
	 */
	public static int[] pack(byte[] buf)
	{
		int k, blen = buf.length, ilen = ((buf.length + 3) >>> 2);
		int[] ibuf = new int[ilen];
		for(int n = 0; n < ilen; n++)
		{
			int m = (n + 1) << 2;
			if(m > blen)
				m = blen;
			for(k = buf[--m] & 0xff; (m & 0x3) != 0; k = (k << 8) | buf[--m] & 0xff)
				;
			ibuf[n] = k;
		}
		return ibuf;
	}
}